A Practical Approach, Second Edition=Ronald D. Ho.pdf

132 DEVELOPMENTAL REPRODUCTIVE TOXICOLOGY: A PRACTICAL APPROACH, SECOND EDITIONtreated adult male rats with saline or cyclophosphamide for 9 weeks and then mated them at variousintervals posttreatment. 71 The high level of postimplantation loss observed after 9 weeks of exposureto cyclophosphamide was markedly decreased by 2 weeks post-treatment and had returned to thecontrol range by 4 weeks posttreatment. Thus, in rats, the male-mediated developmental toxicityof cyclophosphamide was reversible. Moreover, the rate of onset for the actions of cyclophosphamideon progeny outcome was parallel to the rate of reversal.3. HeritabilityAre there adverse effect(s) of paternal drug exposure that persist to subsequent generations in survivingoffspring? Significantly, after paternal cyclophosphamide treatment, increased postimplantation lossand malformations persisted to the F 2 generation; moreover, the malformations observed in the offspringof rats whose fathers were exposed to cyclophosphamide were similar to those found in the F 1 . 66,67,81Behavioral abnormalities caused by paternal cyclophosphamide treatment also persisted in subsequentgenerations. 72,73 Thus, this drug appears to affect spermatogonial stem cells, as well as postmeioticgerm cells, because effects are transmissible to the next generation. There is evidence that this is alsotrue for certain other male-mediated developmental toxicants. A number of the viable congenitalanomalies in the F 1 generation of urethane-treated males were expressed in the F 3 generation. 64 X-rayinduced anomalies have also been shown to be heritable. 64 Thus, germ-line alterations causing malformationscan be transmitted to the next generation as dominant mutations, often with reduced penetrance.No specific chromosomal aberrations were associated with these malformations.While it is clear from animal experiments that exposure of the father to a variety of chemicalscan result in a heritable alteration in his surviving “apparently normal” F 1 progeny, the limitedstudies done to date do not permit us to conclude whether it is valid to extrapolate between species,e.g., from rodents to humans.III. METHODOLOGICAL APPROACHESIN MALE-MEDIATED DEVELOPMENTAL TOXICITYA. Effects of Toxicants in Seminal FluidThe measurement of drugs or chemicals in the seminal fluid can be accomplished fairly readilywith the variety of chemical and physical techniques currently available. We know that drugs canbe transmitted to the female through the semen. One of the tasks facing investigators is theassessment of the consequences to progeny of the presence of drugs or chemicals in seminal fluid.Unless they are bound to spermatozoa, drugs or chemicals in the seminal fluid that enter the femaleare likely to be extensively diluted in the female reproductive tract before they reach the oocyte.Drugs bound either reversibly or irreversibly to spermatozoa may have greater access to theconceptus. Vasectomy experiments are useful in determining whether any effect on progeny outcomeis due to the presence of drug in the seminal fluid or the physical binding of the drug to thespermatozoon that fertilizes the egg. Females can be sequentially mated to a control (fertile) male,and then a drug-treated vasectomized male. Using this approach, it was shown that the effect ofcyclophosphamide after acute administration to male rats was mediated by metabolites of the drugin the seminal fluid, rather than by drug bound to spermatozoa. 33B. Effects on Sperm Quantity and CharacteristicsIdeally, we should like to use the male germ cell itself to evaluate the effects of toxicants with thepotential to cause developmental toxicity to the progeny. Most commonly, toxicants affect malegerm cell numbers, structure, motility, viability, or ability to fertilize the oocyte. 82© 2006 by Taylor & Francis Group, LLC